Do you guys have an idea how they compare in terms of precision? As in how many ppm for the 3/4 circuit from Andreas compared to the one from branadic?
Do you mean precision (repeatability over time + temperature) or accuracy (actual deviation from theoretical value)?
I am not sure whether the values of the datasheet for a 2:1 divider of 1ppm are really accuracy or only precision.
My 2:1 dividers built according to the datasheet have a typical gain of around -9ppm against the ideal value.
But I do not know which (teflone ?) capacitors are used for the 1ppm value.
I use small WIMA MKS-02 mylar capacitors which could be surely improved by low leakage types or even polypropylene.
Further factors on accuracy are the PCB + LTC leakage + charge injection currents and the input bias current of the buffer amplifier at the output.
Interestingly the gain is higher if the pins of the LTC1043 are flipped from the right to the left side. In this case I measure around -2ppm gain which corresponds much more to the calculated error budget of 3.5ppm for the leakage currents with my components.
So I have the suspicion that the charge injection compensation circuit of the LTC1043 works in the wrong direction with the pinning of the LTC datasheet.
With best regards
Andreas